We explore an alternative mechanism for the production of gravitino dark
matter whereby relic gravitinos originate from the decays of superpartners
which are still in thermal equilibrium, i.e. via freeze-in. Contributions to
the gravitino abundance from freeze-in can easily dominate over those from
thermal scattering over a broad range of parameter space, e.g. when the scalar
superpartners are heavy. Because the relic abundance from freeze-in is
independent of the reheating temperature after inflation, collider measurements
may be used to unambiguously reconstruct the freeze-in origin of gravitinos. In
particular, if gravitino freeze-in indeed accounts for the present day dark
matter abundance, then the lifetime of the next-to-lightest superpartner is
uniquely fixed by the superpartner spectrum.Comment: 5 pages, 3 figure
